Heretofore it has been known that frequency agile radar systems incorporating agile magnetrons inherently are plagued with the problem of frequency variation of the magnetron output. Therefore, the local oscillator of the system must be capable of tracking the large frequency excursions in order to maintain a constant intermediate frequency (IF). As is well known to those skilled in the art, such frequency variations and the need to compensate therefore are a result of the mechanical tolerances, temperature variations and the like associated with the radar system.
While numerous approaches have been taken in the past to create an automatic frequency control system for incorporation with frequency agile radar, such systems have generally been expensive to construct and of a complex nature while being of an accuracy below that desirable in sensitive systems.
Consequently, it is an object of the instant invention to present an automatic frequency control circuit for a frequency agile radar which is less expensive to construct, more simplictic in nature and of a greater accuracy than those systems heretofore known.
Still another object of the invention is to present an automatic frequency control circuit for a frequency agile radar system which digitizes the frequency output of the magnetron and digitally compares the same against the desired frequency and creates a digital error signal relative to the required frequency adjustment.
These objects and other objects which will become apparent as the detailed description proceeds are achieved by: a fine correction automatic frequency control circuit for a frequency agile radar system, comprising: pulse generator means connected to said radar system, receiving an IF envelop therefrom, and producing an output pulse of time duration equivalent to a fixed number of periods of the IF; first and second oscillators of different fixed frequencies connected to and controlled by said pulse generator means; error detection means connected to said oscillators for sensing the phase differentials of the output thereof and creating a correction signal for application to said radar system dependent upon said phase differential.